IIP2 calibration is a stringent requirement for a cellular frequency division duplex (FDD) system due to finite isolation between a transmitter and a receiver. Due to a strong dependency between an in-phase path (I-path) and a quadrature-phase path (Q-path) during IIP2 calibration, an exhaustive search to find an optimal digital-to-analog converter (DAC) code that minimizes the I-path and Q-path second order intermodulation (IM2) tone amplitude simultaneously is frequently performed. An exhaustive search may be time consuming.
Alternatively, an iterative search may be performed. However, an iterative search method suffers from a convergence issue within a few iterations due to IQ path dependency.
A searching speed to determine an optimal DAC code that minimizes IM2 tone amplitude may be slower for an apparatus with multiple bands and channels such as a long term evolution (LTE) FDD system. A binary search method to determine the optimal DAC code that minimizes IM2 tone amplitude requires at least 2N searches to determine the optimal DAC code, where N is the number of bits in one calibration code. The effect of second order nonlinearity generates an in-band interference term caused by a leaked transmit signal, which degrades receiver sensitivity.